(231a) Electron-Driven Nitrogen Transformations: Decarbonizing Ammonia Using Plasma Catalysis and Electrochemical Reduction of Nitrate in Wastewaters

Nitrogen fixation in fertilizers forms the basis of modern agriculture and mediates global food insecurity. However, conventional thermally-activated nitrogen conversion processes consume substantial amounts of fossil fuels as materials and energy inputs, leading to an unsustainable energy and carbon footprint. Furthermore, inefficiencies in reactive nitrogen management lead to energy losses as well as hazardous environmental pollution. Therefore, electron-driven approaches are needed to establish fossil-free nitrogen interconversions. Electrochemical and plasma-activated reactions operate under mild conditions, enabling facile coupling to intermittent renewable energy sources to reduce CO₂ emissions and reactive nitrogen pollution, facilitate storage and transportation of renewable energy in nitrogen-based fuels, and improve the global distribution of fertilizer to promote food security. Non-thermal plasma has been used to synthesize ammonia under mild conditions, but the dearth of fundamental understanding of plasma catalytic reactions handicaps the development of efficient plasma catalytic N₂ conversion. Therefore, an in situ FTIR reactor was employed to elucidate the surface reaction mechanisms and plasma-catalyst interactions. A techno-economic analysis revealed the threshold efficiency required for a plasma process to become environmentally and economically competitive. Additionally, electrified membranes (EMs) could provide a scalable means of removing nitrate from water. EMs can extend traditional separation-based membrane properties while also addressing challenges associated with electrochemical nitrate reduction. Conductive membranes functionalized with non-precious metal catalysts showed significantly higher nitrate removal efficiency during electrified filtration compared to diffusion mode. Beyond the environmental impacts of closing the nitrogen loop by converting nitrate into innocuous N₂, selective nitrate reduction to ammonia using modular EMs could partially displace carbon-intensive industrially synthesized ammonia while simultaneously providing water reuse and reactive nitrogen recovery for fertilizer or carbon-free renewable energy storage.